As world-wide energy needs continue to grow, there is concern that demand for energy may outstrip its supply. Technologies for improving the efficiencies of petroleum production become increasingly valuable. Moreover, in light of the impact of petroleum production on the environment, technologies for environmental remediation are also desirable.
Oil extraction from deposits in source rock presently takes place in stages. Typically, the initial stage, known as primary recovery, involves drilling a hole from the surface to a subsurface reservoir, where oil is trapped under pressure. This hole may be known as a well or a wellbore. A subsurface oil reservoir is understood to be an underground pool of a liquid mix of hydrocarbons and other impurities that is contained within a geological formation beneath the surface of the earth. The subsurface reservoir may be penetrated by one or more wells, perforations that contact the subsurface reservoir and permit the removal of the liquid and gas hydrocarbons resident therein. When an oil reservoir containing oil under pressure is tapped by a drill hole, the reservoir's pressure forces its contents through the drill hole to the surface for collection. This process may continue until the pressure within the reservoir is no longer sufficient to expel the oil contained therein. When the pressure in the reservoir is depleted but there is still oil available, pumps may be used to bring the oil to the surface.
The wells used for removing the contents of the reservoir may also be used for injecting substances into the reservoir to enhance the extraction of its contents. For example, such materials as water, brine, steam, and mobilization chemicals such as surfactants may be injected. A well from which oil is recovered is known as a production well. A well through which substances are injected is known as an injection well.
Injection techniques are particularly useful when the pressure within the reservoir decreases so that supplemental measures are useful to increase the recovery of oil contained within the reservoir. Techniques used under these circumstances may be termed secondary recovery techniques. For example, the pressure within the reservoir may be increased by injecting water, steam or gas into the reservoir. Injecting water into a well to increase recovery of oil is called “waterflood.” Other secondary recovery techniques may include flooding with polymers, alkali, or other chemical solutions, and various thermal processes. Alternatively, gases such as carbon dioxide, natural gas or nitrogen may be injected into the reservoir, where they expand and push additional oil out through the production wellbores, and where they may affect the viscosity of the remaining oil, thereby improving its flow rate on egress. The combination of primary and secondary oil recovery only removes a certain amount of the total oil content from an oil reservoir, approximately between 20% and 80%.
Hence, a large amount of the original oil remains in the reservoir after secondary recovery techniques. In large oil fields, over a billion barrels of oil may remain after secondary recovery efforts. The percentage of unrecovered hydrocarbons is largest in oil fields with complex lithologies, and the petroleum fractions left behind tend to be the heavier hydrocarbon materials and those liquid materials that may be trapped by high capillary forces in the micron-sized pores in the reservoir rock or adsorbed onto mineral surfaces through irreducible oil saturation. There may also be pools of bypassed oil within the rock formations surrounding the main reservoir. Retrieving the normally immobile oil residing in the oil field after primary and secondary recovery is referred to herein as “tertiary recovery” or “enhanced oil recovery” (EOR).
Current EOR techniques may be able to remove an additional 5% to 20% of the oil remaining in a reservoir. Techniques currently available leave significant amounts of oil behind. Such techniques may also be expensive to carry out and inefficient. For example, bacteria may be used to free the oil trapped in rock pores or adsorbed onto mineral surfaces, and this freed oil may be dislodged with water during waterflooding. Such bacteria are introduced into the well from external sources. The bacteria may also create methane gas that can be recovered. As another example, gelled or crosslinked water-soluble polymers may be introduced that alter the permeability of geological formations to make waterflooding more effective. Polymers, either preformed or gelled/crosslinked in situ, may be introduced into the reservoir from external sources. Both bacterial techniques and polymer-based techniques are costly processes, though.
As another example, EOR may take place using a variety of externally-introduced chemical agents that may be used to increase the efficacy of waterflooding. These agents fall into two categories. One type of chemical agent may be a surfactant material that can alter the surface tension that adheres oil, water and rock together within the formation. The second type of chemical agent is viscous enough to slow the passage of water through the rock matrix so that the trapped oil can be pushed out more effectively. Chemical techniques for EOR may also be disadvantageous. Existing surfactants, for example, may adversely affect properties of oil-bearing rock formations and thereby damage reservoirs. Also, these surfactants, being of low viscosity, may not be effective in pushing the oil out of the pores where it is trapped. In addition, these surfactants may not be able to function effectively under the high temperature and high pressure conditions where they are used. Certain surfactants, such as petroleum sulfonates or their derivatives, are also particularly difficult to remove from the desired petroleum once it has been extracted. As an additional problem, surfactants are typically used with waterflooding techniques, leading to the production of highly stable emulsions containing mostly water with very little oil. In sum, with existing surfactant techniques, it is difficult to extract oil from rock and difficult to remove it from the water used to flush it out of the reservoir. The costs associated with these processes and their technical limitations have limited the widespread adaptation of these EOR techniques.
Many variations on the aforesaid systems and methods have been proposed. For example, U.S. Patent Appl. No. 20070079964 discloses the use of aliphatic anionic surfactants. U.S. Patent Appl. No. 20060046948 discloses the use of alkyl polyglycosides. U.S. Pat. No. 6,225,263 discloses the use of alkylglycol ethers. U.S. Pat. No. 6,475,290 discloses the use of lignin sulfonates. U.S. Pat. No. 5,911,276 discloses the use of lignin. U.S. Pat. No. 4,790,382 discloses the use of alkylated, oxidized lignin.
In addition to petroleum reservoirs as described above, petroleum may be extracted from formations called oil sands or tar sands. Oil sands, also called tar sands, are mixtures of sand or clay, water and extremely heavy crude oil (e.g., bitumen). For example, a major formation of oil sands in Alberta, Canada, contains material that is approximately 90% sand, 10% crude oil, and water. Oil sand formations are understood to comprise naturally-occurring petroleum deposits in which the lighter fractions of the oil have been lost, and the remaining heavy fractions have been partially degraded by bacteria. The crude oil is extra heavy crude and can be characterized as a naturally occurring viscous mixture of hydrocarbons that are generally heavier than pentane. The petroleum contained in these formations is a viscous, tar-like substance that is admixed with clay, sand and other inorganic particulate matter. Accordingly, it is harder to refine and generally of lesser quality than other crudes. While there is great variability, depending on the oil sands source, the mineral matter in oil sands typically includes a fairly uniform white quartz sand, silt, clay, water, bitumen and other trace minerals, such as zirconium, pyrite and titanium. The bitumen content of oil sands may be as high as 18%, or it can be substantially lower.
As described above, conventional crude oil in reservoirs may be readily extracted by boring wells into the formation, because the light or medium density oil in such reservoirs can flow freely out. By contrast, there is no free-flowing oil in an oil sand formation. Instead, these deposits must be strip mined or their petroleum content must be treated so that it flows.
In the strip mining method, oil sands are dug up from a surface mine and are transported and washed to remove the oil. Mining methods typically involve a number of steps, beginning with excavation and ore size reduction, followed by slurry formation with water and sodium hydroxide. The slurry is then treated with flotation agents (typically kerosene), frothing agents (methylisobutyl carbinol is common), and air is passed through the slurry to create a bitumen froth. This mixture is transported through approximately 2 kilometers of pipeline, creating a mechanical as well as chemical separation of the bitumen from the inorganic sand and silt. The pipeline leads to a separation tank that allows the froth to be skimmed off while the inorganic material falls to the bottom. Since the bitumen is much heavier than standard crude oil, it must be either mixed with a lighter petroleum or chemically processed so that it is flowable enough for transport. Further processing removes water and solids, following which the bitumen may be processed to form synthetic crude oil. Using this method, about two tons of tar sands produce one barrel of oil.
Much of the oil sands reserve is located below the surface, so the strip mining technique is not applicable. For these formations, a variety of in situ methods are available to extract bitumen from underground formations via specialized drilling and extraction techniques. These methods typically use a great amount of energy in the form of steam to heat the trapped bitumen. The heated bitumen has a lower viscosity and can then flow, slowly, to a production well. The steam-softened bitumen forms an emulsion with the water from the steam and drains to a wellhead within the formation from which it is pumped to the surface. This emulsion has similar characteristics to the water-bitumen emulsion produced during strip-mining. The emulsion may be treated similarly, with addition of NaOH and the application of petroleum solvents to make the material flowable.
Mining methods work well for “high-grade” oil sands, i.e., oil sands that have high bitumen content and low clay content. However, such high-grade materials afford a best-case scenario. In reality, the excavated oil sands exist as a mixture of high and low grade materials (“mixed-grade” oil sands). The “low-grade” materials with their lower bitumen content and high clay content are more difficult to extract using conventional methods. It tends to be impractical to separate the low-grade and the high-grade materials within mixed-grade oil sands, so the low-grade materials are simply carried along with the high-grade and not subjected to processing. Increasing production from this type of oil sand can create enormous opportunities for companies that have rights to less desirable grades of oil sands.
Many of the problems that affect oil production, such as those discussed above, also apply to environmental remediation following oil production and other environmental remediation problems, such as may exist following oil spills. Methods have been proposed for dealing with oil spills, such as those disclosed in U.S. Pat. No. 4,925,343 and U.S. Pat. No. 3,788,984.
As well, following petroleum production, there may be discharge of solid materials contaminated with petroleum products. In off-shore deep-water production, oil-laden mud that is wet with sea water must be barged to land, where energy-intensive processing takes place to allow stripping of oil from sand/clay particles and evaporation of water. Only after the mud is cleared of oil can it be dumped into landfill. Despite the inefficiencies, this production scheme is mandated by the EPA. Oil-soaked mud can not simply be put back into the ocean at the point of production without first making sure that all the adhered oil is removed. At present, no technology exists that permits ready stripping of oil from mud within the confines of a production platform.
Materials contaminated with petroleum, its byproducts or residues from its production can have substantial adverse impact on the environment. It would be advantageous to provide economical methods for treating such materials to remove the hydrocarbon contamination in a rapid and effective manner while avoiding the use of chemical or other agents that may inflict further damage on the environment.